Google Docs - I really like Google Docs. I have found it really easy to use for everything from collaborating on papers to collaborating on presentations. I have used it personally to write a published paper with a colleague and to collaboratively write two different presentations for several conference presentations. I also have plans to use it for a group paper assignment for my upcoming technology and teaching course and for a collaborative presentation for the class as well. I have found it really useful and easy to use and the best part is that it is globally portable!!

Google is continuously upgrading Docs to provide an ever-expanding list of great features: http://www.google.com/google-d-s/whatsnew.html . I am especially impressed with the possibilities of Google Forms for creating surveys.